Lesson 4

Question 1

What does loop of Henle do?

Answer 1

• Concentrated Na+ in tissue fluid of medulla
• Causes osmotic flow of water out of collecting ducts and DCTs
• Water then reabsorbed into blood via capillaries of vasa recta
• This concentrates urine with Na+ and makes it hypotonic (lower WP)

Question 2

What happens in asc. limb?

Answer 2

• Na+ and Cl- actively transported out of filtrate in the asc. limb into tissue fluid of medulla
• Lower WP created
• So water leaves desc. limb

Question 3

What happens with desc. limb?

Answer 3

• Water moves by osmosis into capillaries of vasa recta after leaving desc. limb down WP grad
• So filtrate in desc. limb becomes more concentrated as it reaches bottom of loop
• Na+ and Cl- also diffuse back into filtrate near the bottom of loop

Question 4

What is difference between asc. and desc. limb?

Answer 4

AL is impermeable to water whereas DL is permeable

Question 5

What happens to water in collecting duct?

Answer 5

It leaves ducts by osmosis to be reabsorbed into the surrounding tissue fluid in the DCT and collecting ducts which is hypotonic

Question 6

What does antidiuretic hormone (ADH) do?

Answer 6

• Increased permeability of duct walls and DCT cells to water
• It causes more aquaporins to be incorporated in plasma membranes

Question 7

Describe negative feedback involving ADH

Answer 7

• Osmoreceptors in hypothalamus detect changed in WP of blood
• Cells of posterior lobe of pituitary gland secrete more or less ADH in response to detection
• Cells of DCT and collecting ducts will become more or less permeable to water depending on change

Question 8

Describe what happens if man is dehydrated

Answer 8

• Osmoreceptors in hypothalamus detect decrease in WP of blood
• Nerve impulses sent to posterior lobe of pituitary gland
• So more ADH released and go to collecting ducts in nephrons
• Cells of duct walls become more permeable and more water leaves filtrate
• So small volume of concentrated urine produced